Certain vehicle control systems involve measuring pressure parameters, such as engine oil pressure, fuel pressure, transmission fluid pressure, or brake pressure. Silicon-based pressure sensors, for example, are used in a wide variety of automotive applications, including sensing manifold absolute pressure (MAP), turbo intake air pressure, and differential fuel vapor pressure. In addition, some occupant detection systems incorporate silicon-based pressure sensors.
Some silicon-based pressure sensors, known as absolute silicon-based pressure sensors, work by sensing a differential pressure across a thin silicon membrane or diaphragm within a cell body. The silicon membrane and cell body form a cavity that is hermetically sealed under a vacuum. This cavity establishes a reference pressure on one side of the membrane. The pressure sensor outputs a voltage that is proportional to the difference in pressure between the sensed pressure and the reference pressure. To provide acceptable service, the cell body and corresponding package must be able to withstand the environment.
In some absolute silicon-based pressure sensors, plastic packages with silicone adhesives are used to maintain the differential pressure across the diaphragm. These structures can be used when pressures are on the order of, for example, a few atmospheres. In high pressure or other harsh environments, however, media appropriate materials must be used for the packaging. Examples of such materials include, for example, solder, stainless steel, and ceramic. Some silicon-based pressure sensors use conventional ceramic, oil-filled TO cans as packaging materials that allow high pressure or other harsh environment operation. Using conventional manufacturing techniques, each sensor is manufactured serially, that is, one at a time.